#include <cstdio>
#include <algorithm>
#include<vector>
#include<queue>

using namespace std;

int nod,minim,i,aux,n,k,j,p,s,unu,t,m,doi,x,st,dr,maxi,sol,maxi2,viz[50010],y,conex,cost,d[50010],ok;
vector < pair<int, int> > v[50010];
int x1,x2;

struct cmp
{
    bool operator() (int x,int y)
    {
        return d[x]>d[y];
    }
};

priority_queue<int,vector <int>,cmp> q;




int main()
{
    freopen ("pscnv.in","r",stdin);
    freopen ("pscnv.out","w",stdout);
    scanf("%d%d%d%d",&n,&m,&x1,&x2);
    for(i=1;i<=m;i++)
    {
        scanf("%d %d %d",&x,&y,&cost);
       // printf("%d %d %d\n",x,y,cost);
        v[x].push_back(make_pair(y,cost));
    }
     for(i=1;i<=n;i++)
    {
        d[i]=100000000;
    }
    d[x1]=0;
    q.push(x1);


    while(! q.empty() )//&& d[x2]==100000000
    {
        nod=q.top();
        q.pop();
       // printf("%d\n",nod);
        for(i=0;i<v[nod].size();i++)
        {
            if(d[v[nod][i].first] >v[nod][i].second)
            {
                d[v[nod][i].first] = v[nod][i].second;
                q.push(v[nod][i].first);
            }
        }
    }

    for(i=1;i<=n;i++)
    {
       // printf("%d ",d[i]);
    }
    printf("%d\n",d[x2]);
}